Transversely-excited film bulk acoustic resonator matrix filters with switches in parallel with sub-filter shunt capacitors

ABSTRACT

There are disclosed matrix filters having an input port and sub-filters connected between the input port and respective output ports. Each of the sub-filters includes a ladder circuit with n transversely-excited film bulk acoustic resonator (XBAR) series elements and n−1 capacitor shunt elements, where n, the order of the sub-filter, is an integer greater than 2. Each sub-filter further has a first switch in parallel with a first capacitor shunt element and a second switch in parallel with a last capacitor shunt element.

RELATED APPLICATION INFORMATION

This patent is a continuation of Ser. No. 17/373,427, filed Jul. 12,2021, titled TRANSVERSELY-EXCITED FILM BULK ACOUSTIC RESONATOR MATRIXFILTERS WITH SWITCHES IN PARALLEL WITH SUB-FILTER SHUNT CAPACITORS,which is a continuation-in-part of application Ser. No. 17/372,114,filed Jul. 9, 2021, titled TRANSVERSELY-EXCITED FILM BULK ACOUSTICRESONATOR MATRIX FILTERS WITH NONCONTIGUOUS PASSBAND, which is claimspriority from provisional patent application 63/180,084, filed Apr. 27,2021, entitled MATRIX FILTER FOR RF DIVERSITY RECEIVER and is acontinuation-in-part of application Ser. No. 17/122,986, filed Dec. 15,2020, titled ACOUSTIC MATRIX DIPLEXERS AND RADIOS USING ACOUSTIC MATRIXDIPLEXERS, which is a continuation-in-part of application Ser. No.17/121,724, filed Dec. 14, 2020, titled ACOUSTIC MATRIX FILTERS ANDRADIOS USING ACOUSTIC MATRIX FILTERS, which claims priority fromprovisional patent application 63/087,789, filed Oct. 5, 2020, entitledMATRIX XBAR FILTER. All of these applications are incorporated herein byreference.

NOTICE OF COPYRIGHTS AND TRADE DRESS

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. This patent document may showand/or describe matter which is or may become trade dress of the owner.The copyright and trade dress owner has no objection to the facsimilereproduction by anyone of the patent disclosure as it appears in thePatent and Trademark Office patent files or records, but otherwisereserves all copyright and trade dress rights whatsoever.

BACKGROUND Field

This disclosure relates to radio frequency filters using acoustic waveresonators, and specifically to filters for use in communicationsequipment.

Description of the Related Art

A radio frequency (RF) filter is a two-port device configured to passsome frequencies and to stop other frequencies, where “pass” meanstransmit with relatively low signal loss and “stop” means block orsubstantially attenuate. The range of frequencies passed by a filter isreferred to as the “pass-band” of the filter. The range of frequenciesstopped by such a filter is referred to as the “stop-band” of thefilter. A typical RF filter has at least one pass-band and at least onestop-band. Specific requirements on a passband or stop-band depend onthe specific application. For example, a “pass-band” may be defined as afrequency range where the insertion loss of a filter is better than adefined value such as 1 dB, 2 dB, or 3 dB. A “stop-band” may be definedas a frequency range where the rejection of a filter is greater than adefined value such as 20 dB, 30 dB, 40 dB, or greater depending onapplication.

RF filters are used in communications systems where information istransmitted over wireless links. For example, RF filters may be found inthe RF front-ends of cellular base stations, mobile telephone andcomputing devices, satellite transceivers and ground stations, IoT(Internet of Things) devices, laptop computers and tablets, fixed pointradio links, and other communications systems. RF filters are also usedin radar and electronic and information warfare systems.

RF filters typically require many design trade-offs to achieve, for eachspecific application, the best compromise between performance parameterssuch as insertion loss, rejection, isolation, power handling, linearity,size and cost. Specific design and manufacturing methods andenhancements can benefit simultaneously one or several of theserequirements.

Performance enhancements to the RF filters in a wireless system can havebroad impact to system performance. Improvements in RF filters can beleveraged to provide system performance improvements such as larger cellsize, longer battery life, higher data rates, greater network capacity,lower cost, enhanced security, higher reliability, etc. Theseimprovements can be realized at many levels of the wireless system bothseparately and in combination, for example at the RF module, RFtransceiver, mobile or fixed sub-system, or network levels.

High performance RF filters for present communication systems commonlyincorporate acoustic wave resonators including surface acoustic wave(SAW) resonators, bulk acoustic wave (BAW) resonators, film bulkacoustic wave resonators (FBAR), and other types of acoustic resonators.However, these existing technologies are not well-suited for use at thehigher frequencies and bandwidths proposed for future communicationsnetworks.

The desire for wider communication channel bandwidths will inevitablylead to the use of higher frequency communications bands. Radio accesstechnology for mobile telephone networks has been standardized by the3GPP (3^(rd) Generation Partnership Project). Radio access technologyfor 5^(th) generation mobile networks is defined in the 5G NR (newradio) standard. The 5G NR standard defines several new communicationsbands. Two of these new communications bands are n77, which uses thefrequency range from 3300 MHz to 4200 MHz, and n79, which uses thefrequency range from 4400 MHz to 5000 MHz. Both band n77 and band n79use time-division duplexing (TDD), such that a communications deviceoperating in band n77 and/or band n79 use the same frequencies for bothuplink and downlink transmissions. Bandpass filters for bands n77and n79must be capable of handling the transmit power of the communicationsdevice. WiFi bands at 5GHz and 6GHz also require high frequency and widebandwidth. The 5G NR standard also defines millimeter wave communicationbands with frequencies between 24.25 GHz and 40 GHz.

The Transversely-Excited Film Bulk Acoustic Resonator (XBAR) is anacoustic resonator structure for use in microwave filters. The XBAR isdescribed in U.S. Pat. No. 10,491,291, titled TRANSVERSELY EXCITED FILMBULK ACOUSTIC RESONATOR. An XBAR resonator comprises an interdigitaltransducer (IDT) formed on a thin floating layer, or diaphragm, of asingle-crystal piezoelectric material. The IDT includes a first set ofparallel fingers, extending from a first busbar and a second set ofparallel fingers extending from a second busbar. The first and secondsets of parallel fingers are interleaved. A microwave signal applied tothe IDT excites a shear primary acoustic wave in the piezoelectricdiaphragm. XBAR resonators provide very high electromechanical couplingand high frequency capability. XBAR resonators may be used in a varietyof RF filters including band-reject filters, band-pass filters,duplexers, and multiplexers. XBARs are well suited for use in filtersfor communications bands with frequencies above 3 GHz. Matrix XBARfilters are also suited for frequencies between 1 GHz and 3 GHz.

DESCRIPTION OF THE DRAWINGS

FIG. 1 includes a schematic plan view, two schematic cross-sectionalviews, and a detailed cross-sectional view of a transversely-excitedfilm bulk acoustic resonator (XBAR).

FIG. 2A is an equivalent circuit model of an acoustic resonator.

FIG. 2B is a graph of the admittance of an ideal acoustic resonator.

FIG. 2C is a circuit symbol for an acoustic resonator.

FIG. 3A is a schematic diagram of a matrix filter using acousticresonators.

FIG. 3B is a schematic diagram of a sub-filter of FIG. 3A.

FIG. 4 is a graph of the performance of an embodiment of the filter ofFIG. 3A showing resonant frequencies of the sub-filters.

FIG. 5 is the graph of the performance of the embodiment of the filterof FIG. 3A showing passband frequencies of the sub-filters.

FIG. 6 is a schematic diagram of a matrix diplexer using acousticresonators.

FIG. 7 is a graph of input-output transfer functions of an embodiment ofthe switched diplexer of FIG. 6 .

FIG. 8 is a schematic diagram of a matrix triplexer using acousticresonators.

FIG. 9 is a graph of input-output transfer functions of an embodiment ofthe triplexer of FIG. 8 .

FIG. 10A is a schematic diagram of a reconfigurable switched matrixfilter using acoustic resonators.

FIG. 10B is a schematic diagram of a sub-filter and switch module ofFIG. 10A.

FIG. 11 is a graph of input-output transfer functions of twoconfigurations of an embodiment of the reconfigurable switched matrixfilter of FIG. 10A.

FIG. 12 is a block diagram of a three-band time division duplex radiousing a switched matrix triplexer.

FIG. 13 is a block diagram of a three-band diversity receiver using amatrix triplexer.

Throughout this description, elements appearing in figures are assignedthree-digit or four-digit reference designators, where the two leastsignificant digits are specific to the element and the one or two mostsignificant digit is the figure number where the element is firstintroduced. An element that is not described in conjunction with afigure may be presumed to have the same characteristics and function asa previously-described element having the same reference designator.

DETAILED DESCRIPTION

Description of Apparatus

FIG. 1 shows a simplified schematic top view, orthogonal cross-sectionalviews, and a detailed cross-sectional view of a transversely-excitedfilm bulk acoustic resonator (XBAR) 100. XBAR resonators such as theresonator 100 may be used in a variety of RF filters includingband-reject filters, band-pass filters, duplexers, and multiplexers.XBARs are particularly suited for use in filters for communicationsbands with frequencies above 3 GHz. The matrix XBAR filters described inthis patent are also suited for frequencies above 1 GHz.

The XBAR 100 is made up of a thin film conductor pattern formed on asurface of a piezoelectric plate 110 having parallel front and backsurfaces 112, 114, respectively. The piezoelectric plate is a thinsingle-crystal layer of a piezoelectric material such as lithiumniobate, lithium tantalate, lanthanum gallium silicate, gallium nitride,or aluminum nitride. The piezoelectric plate is cut such that theorientation of the X, Y, and Z crystalline axes with respect to thefront and back surfaces is known and consistent. The piezoelectric platemay be Z-cut (which is to say the Z axis is normal to the front and backsurfaces 112, 114), rotated Z-cut, or rotated YX cut. XBARs may befabricated on piezoelectric plates with other crystallographicorientations.

The back surface 114 of the piezoelectric plate 110 is attached to asurface of the substrate 120 except for a portion of the piezoelectricplate 110 that forms a diaphragm 115 spanning a cavity 140 formed in thesubstrate. The portion of the piezoelectric plate that spans the cavityis referred to herein as the “diaphragm” 115 due to its physicalresemblance to the diaphragm of a microphone. As shown in FIG. 1 , thediaphragm 115 is contiguous with the rest of the piezoelectric plate 110around all of a perimeter 145 of the cavity 140. In this context,“contiguous” means “continuously connected without any interveningitem”. In other configurations, the diaphragm 115 may be contiguous withthe piezoelectric plate around at least 50% of the perimeter 145 of thecavity 140.

The substrate 120 provides mechanical support to the piezoelectric plate110. The substrate 120 may be, for example, silicon, sapphire, quartz,or some other material or combination of materials. The back surface 114of the piezoelectric plate 110 may be bonded to the substrate 120 usinga wafer bonding process. Alternatively, the piezoelectric plate 110 maybe grown on the substrate 120 or attached to the substrate in some othermanner. The piezoelectric plate 110 may be attached directly to thesubstrate or may be attached to the substrate 120 via one or moreintermediate material layers (not shown in FIG. 1 ).

“Cavity” has its conventional meaning of “an empty space within a solidbody.” The cavity 140 may be a hole completely through the substrate 120(as shown in Section A-A and Section B-B) or a recess in the substrate120 under the diaphragm 115. The cavity 140 may be formed, for example,by selective etching of the substrate 120 before or after thepiezoelectric plate 110 and the substrate 120 are attached.

The conductor pattern of the XBAR 100 includes an interdigitaltransducer (IDT) 130. The IDT 130 includes a first plurality of parallelfingers, such as finger 136, extending from a first busbar 132 and asecond plurality of fingers extending from a second busbar 134. Thefirst and second pluralities of parallel fingers are interleaved. Theinterleaved fingers overlap for a distance AP, commonly referred to asthe “aperture” of the IDT. The center-to-center distance L between theoutermost fingers of the IDT 130 is the “length” of the IDT.

The first and second busbars 132, 134 serve as the terminals of the XBAR100. A radio frequency or microwave signal applied between the twobusbars 132, 134 of the IDT 130 excites a primary acoustic mode withinthe piezoelectric plate 110. The primary acoustic mode of an XBAR is abulk shear mode where acoustic energy propagates along a directionsubstantially orthogonal to the surface of the piezoelectric plate 110,which is also normal, or transverse, to the direction of the electricfield created by the IDT fingers. Thus, the XBAR is considered atransversely-excited film bulk wave resonator.

The IDT 130 is positioned on the piezoelectric plate 110 such that atleast the fingers of the IDT 130 are disposed on the diaphragm 115 ofthe piezoelectric plate which spans, or is suspended over, the cavity140. As shown in FIG. 1 , the cavity 140 has a rectangular shape with anextent greater than the aperture AP and length L of the IDT 130. Acavity of an XBAR may have a different shape, such as a regular orirregular polygon. The cavity of an XBAR may have more or fewer thanfour sides, which may be straight or curved.

The detailed cross-section view (Detail C) shows two IDT fingers 136 a,136 b on the surface of the piezoelectric plate 110. The dimension p isthe “pitch” of the IDT and the dimension w is the width or “mark” of theIDT fingers. A dielectric layer 150 may be formed between and optionallyover (see IDT finger 136 a) the IDT fingers. The dielectric layer 150may be a non-piezoelectric dielectric material, such as silicon dioxideor silicon nitride. The dielectric layer 150 may be formed of multiplelayers of two or more materials. The IDT fingers 136 a and 136 b may bealuminum, copper, beryllium, gold, tungsten, molybdenum, alloys andcombinations thereof, or some other conductive material. Thin (relativeto the total thickness of the conductors) layers of other metals, suchas chromium or titanium, may be formed under and/or over and/or aslayers within the fingers to improve adhesion between the fingers andthe piezoelectric plate 110 and/or to passivate or encapsulate thefingers and/or to improve power handling. The busbars of the IDT 130 maybe made of the same or different materials as the fingers.

For ease of presentation in FIG. 1 , the geometric pitch and width ofthe IDT fingers is greatly exaggerated with respect to the length(dimension L) and aperture (dimension AP) of the XBAR. A typical XBARhas more than ten parallel fingers in the IDT 110. An XBAR may havehundreds of parallel fingers in the IDT 110. Similarly, the thickness ofthe fingers in the cross-sectional views is greatly exaggerated.

An XBAR based on shear acoustic wave resonances can achieve betterperformance than current state-of-the art surface acoustic wave (SAW),film-bulk-acoustic-resonators (FBAR), and solidly-mounted-resonatorbulk-acoustic-wave (SMR BAW) devices. In particular, the piezoelectriccoupling for shear wave XBAR resonances can be high (>20%) compared toother acoustic resonators. High piezoelectric coupling enables thedesign and implementation of microwave and millimeter-wave filters ofvarious types with appreciable bandwidth.

The basic behavior of acoustic resonators, including XBARs, is commonlydescribed using the Butterworth Van Dyke (BVD) circuit model as shown inFIG. 2A. The BVD circuit model consists of a motional arm and a staticarm. The motional arm includes a motional inductance L_(m), a motionalcapacitance C_(m), and a resistance R_(m). The static arm includes astatic capacitance C₀ and a resistance R₀. While the BVD model does notfully describe the behavior of an acoustic resonator, it does a good jobof modeling the two primary resonances that are used to design band-passfilters, duplexers, and multiplexers (multiplexers are filters with morethan 2 input or output ports with multiple passbands).

The first primary resonance of the BVD model is the motional resonancecaused by the series combination of the motional inductance L_(m) andthe motional capacitance C_(m). The second primary resonance of the BVDmodel is the anti-resonance caused by the combination of the motionalinductance L_(m), the motional capacitance C_(m), and the staticcapacitance C₀. In a lossless resonator (R_(m)=R₀=0), the frequencyF_(r) of the motional resonance is given by

$\begin{matrix}{F_{r} = \frac{1}{2\pi\sqrt{L_{m}C_{m}}}} & (1)\end{matrix}$

The frequency F_(a) of the anti-resonance is given by

$\begin{matrix}{F_{a} = {F_{r}\sqrt{1 + \frac{1}{\gamma}}}} & (2)\end{matrix}$

where γ=C₀/C_(m) is dependent on the resonator structure and the typeand the orientation of the crystalline axes of the piezoelectricmaterial.

FIG. 2B is a graph 200 of the magnitude of admittance of a theoreticallossless acoustic resonator. The acoustic resonator has a resonance 212at a resonance frequency where the admittance of the resonatorapproaches infinity. The resonance is due to the series combination ofthe motional inductance L_(m) and the motional capacitance C_(m) in theBVD model of FIG. 2A. The acoustic resonator also exhibits ananti-resonance 214 where the admittance of the resonator approacheszero. The anti-resonance is caused by the combination of the motionalinductance L_(m), the motional capacitance C_(m), and the staticcapacitance C₀. In a lossless resonator (R_(m)=R₀=0), the frequencyF_(r) of the resonance is given by

$\begin{matrix}{F_{r} = \frac{1}{2\pi\sqrt{L_{m}C_{m}}}} & (1)\end{matrix}$

The frequency F_(a) of the anti-resonance is given by

$\begin{matrix}{F_{a} = {F_{r}\sqrt{1 + \frac{1}{\gamma}}}} & (2)\end{matrix}$

In over-simplified terms, the lossless acoustic resonator can beconsidered a short circuit at the resonance frequency 212 and an opencircuit at the anti-resonance frequency 214. The resonance andanti-resonance frequencies in FIG. 2B are representative, and anacoustic resonator may be designed for other frequencies.

FIG. 2C shows the circuit symbol for an acoustic resonator such as anXBAR. This symbol will be used to designate each acoustic resonator inschematic diagrams of filters in subsequent figures.

FIG. 3A is a schematic diagram of a matrix filter 300 using acousticresonators. The matrix filter 300 includes an array 310 of n sub-filters320-1, 320-2, 320-n connected in parallel between a first filter port(FP1) and a second filter port (FP2), where n is an integer greater thanone. The sub-filters 320-1, 320-2, 320-n may have contiguous passbandssuch that the bandwidth of the matrix filter 300 is equal to the sum ofthe bandwidths of the constituent sub-filters. An example of sub-filterswith contiguous passbands is described in U.S. patent application Ser.No. 17/362,727 filed Jun. 29, 2021, entitled TRANSVERSELY-EXCITED FILMBULK ACOUSTIC RESONATOR MATRIX FILTERS WITH SPLIT DIE SUB-FILTERS whichis incorporated herein by reference. The sub-filters 320-1, 320-2, 320-nmay have noncontiguous passbands such that the bandwidth of the matrixfilter 300 is not equal to the sum of the bandwidths of the constituentsub-filters, but instead has three separate and independent passbandsseparated by stop bands that exist where the input-output transferfunction of the matrix filter 300 is less than −20 dB. In the subsequentexamples in this patent, the sub-filters have non-contiguous passbandsand n=3. n can be less than or greater than 3 as necessary to providethe desired noncontiguous passbands for the matrix filter 300. In somecases, the n sub-filters 320-1, 320-2, 320-n may include one or moreXBARs. The filter 300 and/or sub-filters may be RF filters that passfrequency bands defined by the 5G NR standard.

The array 310 of sub-filters is terminated at the FP1 end by acousticresonators XL1 and XH1, which are preferably but not necessarily XBARs.The array 310 of sub-filters is terminated at the FP2 end by acousticresonators XL2 and XH2, which are preferably but not necessarily XBARs.The acoustic resonators XL1, XL2, XH1, and XH2 create “transmissionzeros” at their respective resonance frequencies. A “transmission zero”is a frequency where the input-output transfer function of the filter300 is very low (and would be zero if the acoustic resonators XL1, XL2,XH1, and XH2 were lossless). The zero transmission may be caused by oneor more of the acoustic resonators creating a very low impedance toground and thus, in this configuration cause the sub-filters to beremoved as filtering components as the acoustic resonators are basicallyshort circuits to ground so that the sub-filters have no effect on thefilter 300 during transmission zero frequencies. Typically, but notnecessarily, the resonance frequencies of XL1 and XL2 are equal, and theresonance frequencies of XH1 and XH2 are equal. The resonant frequenciesof the acoustic resonators XL1, XL2 are selected to provide transmissionzeros adjacent to the lower edge of the filter passband. XL1 and XL2 maybe referred to as “low-edge resonators” since their resonant frequenciesare proximate the lower edge of the filter passband. The acousticresonators XL1 and XL2 also act as shunt inductances to help match theimpedance at the ports of the filter to a desired impedance value. Inthe subsequent examples in this patent, the impedance at all ports ofthe filters is matched to 50 ohms. The impedance may be another value ifdesired, such as 20, 100 or 1000 ohms. The resonant frequencies ofacoustic resonators XH1, XH2 are selected to provide transmission zerosat or above the higher edge of the filter passband. XH1 and XH2 may bereferred to as “high-edge resonators” since their resonant frequenciesare proximate the higher edge of the filter pas sband. High-edgeresonators XH1 and XH2 may not be required in all matrix filters, suchas filters that have sub-filters that will not pass a relative amplitudeof signals at these high edge frequencies.

FIG. 3B is a schematic diagram of a sub-filter 350 suitable for each ofsub-filters 320-1, 320-2, and 320-n of filter 300. The sub-filter 350includes three acoustic resonators XA, XB, XC connected in seriesbetween a first sub-filter port (SP1) which can be connected to FP1 anda second sub-filter port (SP2) which can be connected to FP2. Theacoustic resonators XA, XB, XC are preferably but not necessarily XBARs.The sub-filter 350 includes two coupling capacitors CA, CB, each ofwhich is connected between ground and a respective node between two ofthe acoustic resonators. The inclusion of three acoustic resonators inthe sub-filter 350 is exemplary. A sub-filter may have m acousticresonators, where m is an integer greater than one. A sub-filter with macoustic resonators includes m−1 coupling capacitors. The in acousticresonators of a sub-filter are connected in series between the two portsSP1 and SP2 of a sub-filter and each of the m−1 coupling capacitors isconnected between ground and a node between a respective pair ofacoustic resonators from the in acoustic resonators.

Compared to other types of acoustic resonators, XBARs have very highelectromechanical coupling (which results in a large difference betweenthe resonance and anti-resonance frequencies), but low capacitance perunit area. The matrix filter architecture, as shown in FIG. 3A and FIG.3B, takes advantage of the high electromechanical coupling of XBARswithout requiring high resonator capacitance.

FIG. 4 is a graph 400 of the performance 405 of an exemplary embodimentof a matrix filter implemented using XBARs for all of the acousticresonators. The performance 405 in graph 400 may be performance of thetransfer function S21 for filter 300 having 3 non-continuous passbandsub-filters 1, 2 and 3. Specifically, performance 405 includes thesolid, dashed and dotted lines 410, 420 and 430 that are a plot of S21,the FP1 to FP2 transfer function, of the filter as a function offrequency where each of lines 410, 420 and 430 are for non-continuouspassband sub-filters 1, 2 and 3, respectively. That is, the solid line410 is a plot of S21, the FP1 to FP2 separate transfer function forsub-filter 1 of the filter as a function of frequency and with resonancefrequency SF1 in isolation. The dashed line 420 is a plot of S21, theFP1 to FP2 separate transfer function for sub-filter 2 of the filter asa function of frequency and with resonance frequency SF2 in isolation.The dotted line 430 is a plot of S21, the FP1 to FP2 separate transferfunction for sub-filter 3 of the filter as a function of frequency andwith resonance frequency SF3 in isolation. Since the exemplary filter issymmetrical, the solid, dashed and dotted lines 410, 420 and 430 arealso plots of S12.

FIG. 5 is a graph 500 of the passband frequencies of the sub-filterswithin the exemplary matrix filter of the filter of FIG. 3A whoseperformance was shown in FIG. 4 . The example of graph 500 may be forthe receive frequencies of LTE bands 3, 1, and 7 (from low to highfrequency) with pass bands defined as above −3 dB. Specifically, P1, P2,and P3 are passband frequencies above −3 dB of the magnitude of theinput-output transfer functions for sub-filter 1, sub-filter 2, andsub-filter 3, respectively. Passbands P1, P2, and P3 are noncontiguousbecause each pair of adjacent passbands is separated by a stop bandwhere the input-output transfer function of the matrix filter is lessthan −20 dB. For instance, passbands P1 and P2 are noncontiguous becausethat pair is separated by stop band SB1 that exist where theinput-output transfer function S21 of the matrix filter 300 is less than−20 dB. Also, passbands P2 and P3 are noncontiguous because that pair isseparated by stop band SB2 that exist where the input-output transferfunction S21 of the matrix filter 300 is less than −20 dB. As notedabove, this application also considers embodiments where the sub-filters320-1, 320-2, 320-n may have contiguous passbands.

The matrix filter for FIGS. 4 and 5 includes 3 sub-filters withconnections between input and output ports that can be switched in andout to provide numerous passbands for input and output RF communicationsignals. Each sub-filter may include three XBARs, as shown in FIG. 3Aand FIG. 3B. In other cases, there may be two, four, five or up to 10sub-filters. Also, each sub-filter may include more than three XBARs and2 coupling capacitors. Some sub-filters may have m acoustic resonatorswhere m=four, five, six or up to 10; and a corresponding m−1 couplingcapacitors as noted for FIG. 3B. In this example and all subsequentexamples, filter performance was determined by simulating the filterusing BVD models (FIG. 2A) for the XBARs. It can be appreciated that theconcepts herein regarding 3 sub-filters can be expanded to only two orup to four, five or up to an arbitrary number determined by size androuting complexity considerations.

The input-output transfer function of the exemplary filter, as shown inFIG. 4 , is the vector sum of the input-output transfer functions of thethree sub-filters, where the three sub-filters have noncontiguouspassbands. Noncontiguous passbands may mean that no single sub-filterinput-output transfer function crosses another sub-filter input-outputtransfer function at a frequency where both filters S21 transferfunctions are above −20 dB. To this end, the input-output transferfunctions of sub-filter 1 and sub-filter 2 cross at a frequency justbelow 2 GHz where (a) S21 of both filters are not above −20 dB and (b)the phases of the input-output transfer functions of both filters aresubstantially equal. In this context, “not above” means sufficientlybelow to not cause objectionable variations in either of the transferfunctions of a sub-filter due to the transfer function of a differentsub-filter of the matrix filter within the filter passband ranges, whichis this case is 1.5 to 3 GHz. The quantitative value of “not above” maybe different for different filter applications. Similar requirementsapply to sub-filter 2 and sub-filter 3. In matrix filters with more thanthree sub-filters, similar requirements apply to every adjacent (infrequency) pair of sub-filters.

In some cases, a “contiguous” passband matrix filter describes matrixfilters having a passband that is the sum of the passbands of more thanone sub-filter, while a “noncontiguous” passband matrix filter describesmatrix filters where each passband is the passband of only onesub-filter. For some switched matrix filters, the passbands of thesub-filters of a “noncontiguous” are not adjacent or do not overlapabove −20 dB. A matrix filter may also have some sub-filters that arecontiguous and other sub-filters that are noncontiguous. For example, itmay be a filter having at least one stop band between passbands of atleast one pair of adjacent sub-filters.

In one example, the lowest passband, noncontiguous passband sub-filter1, is LTE band Rx 3 and has 3 resonators and 2 coupling capacitors.Here, the middle passband, noncontiguous passband sub-filter 2, is LTEband Rx 1 and has 5 resonators and 4 coupling capacitors. The highestpassband, noncontiguous passbands sub-filter 3, is LTE band Rx 7 andsub-filter has 4 resonators and 3 coupling capacitors. This filter mayhave one or more XL resonators and zero or more XH resonators.

The exemplary matrix filter is symmetrical in that the impedances atPort 1 and Port 2 are both equal to 50 ohms. Matrix filters may also bedesigned to have significantly different impedances at Port 1 and Port2, in which event the internal circuitry will not be symmetrical. Thevertical dot-dash lines identify the resonance frequencies of the XBARswithin the exemplary matrix filter. The line labeled “XL” identifies theresonance frequency of the resonators XL1 and XL2, which is adjacent tothe lower edge of the filter passband. Similarly, the line labeled “XH”identifies the resonance frequency of the resonators XH1 and XH2, whichis adjacent to the upper edge of the filter passband. The two lineslabeled “SF1” in FIG. 4 identify the resonance frequencies of the XBARswithin sub-filter 1 in isolation. The two lines labeled “PBF1” in FIG. 5identify the passband frequencies of the XBARs within sub-filter 1 inisolation. Note that both of the resonance frequencies are lower thanthe center of the passband. This is because the resonance frequency of aresonator and a capacitor in series is higher that the resonancefrequency of the resonator in isolation. Similarly, the two lineslabeled “SF2” identify the resonance frequencies of the XBARs withinsub-filter 2 and the two lines labeled “SF3” identify the resonancefrequencies of the XBARs within sub-filter 3. Similarly, the two lineslabeled “SF2” in FIG. 4 identify the resonance frequencies and two lineslabeled “PBF2” in FIG. 5 identify the passband frequencies of the XBARswithin sub-filter 2. Finally, the two lines labeled “SF3” in FIG. 4identify the resonance frequencies and two lines labeled “PBF3” in FIG.5 identify the passband frequencies of the XBARs within sub-filter 3.

FIG. 6 is a schematic diagram of a matrix filter 600 configured as adiplexer. The matrix filter 600 includes an array 610 of threesub-filters 620-1, 620-2, 620-n. Sub-filter 1 620-1 is connected betweena first filter port (FP1) and a second filter port (FP2). Sub-filter 2620-2 and sub-filter 3 620-3 are connected in parallel between FP1 and athird filter port (FP3). FP1 is the common or input port of the diplexerand FP2 and FP3 are the branch or output ports. The array 610 ofsub-filters is terminated at both ends by XBARs XL and XH as previouslydescribed.

FIG. 7 is a graph 700 of the performance 705 of an example of the matrixfilter diplexer 600 of FIG. 6 . In this example, XL, XH, and the threesub-filters are the same as the corresponding elements of the matrixfilter 300 of FIG. 3A. In FIG. 7 , the solid line 410 under 710 is aplot of S21, the FP1 to FP2 transfer function, as a function offrequency. The dashed line 420 and dotted line 430 under 720 is a plotof S31, the FP1 to FP3 transfer function, as a function of frequency.Since the exemplary filter is symmetrical, the solid line 410 under 710and the dashed line 420 and dotted line 430 under 720 are also plots ofS12 and S13, respectively. The switched matrix filter 600 is exemplary.In most applications, a diplexer will have the same number (two, threeor more) sub-filters in parallel between the common port and the twobranch ports.

FP1 may be considered the common port of the matrix filter diplexer 600.FP2 may be considered the “low band” port and FP3 may be considered the“high band” port. When the matrix filter diplexer is used in a frequencydivision duplex radio, one of FP2 and FP3 may be the receive port of thediplexer and the other of FP2 and FP3 may be the transmit port of thediplexer depending on the frequencies allocated for reception andtransmission.

In a second diplexer configuration that is a variant of filter 600,sub-filter 1 620-1 and sub-filter 2 620-2 are connected in parallelbetween FP1 and a FP2. Here, sub-filter 3 620-3 is connected between aFP1 and a FP3. In this case, a graph of the performance of an example ofthe matrix filter diplexer has the solid line 410 and dashed line 420 asa plot of S21; and the dotted line 430 as a plot of S31, as a functionof frequency.

In a third diplexer configuration that is a variant of filter 600,sub-filter 1 620-1 and sub-filter 3 620-3 are connected in parallelbetween FP1 and FP2. Here, sub-filter 2 620-2 is connected between FP1and FP3. In this case, a graph of the performance of an example of theswitched matrix filter diplexer has the solid line 410 and dotted line430 as a plot of S21; and the dashed line 420 as a plot of S31, as afunction of frequency.

The diplexer sfilter 600 and two variants are switched matrix filtersbecause any one of the branch ports FP2 or FP3 may be selected orswitched to as an output for the filter. For example, the sub-filtersconnections between input and output ports can be switched in and out toprovide numerous passbands for input and output RF communicationsignals.

FIG. 8 is a schematic diagram of a matrix triplexer filter 800 usingacoustic resonators. The matrix filter 800 includes an array 810 ofthree sub-filters 820-1, 820-2, 820-n. Sub-filter 1 820-1 is connectedbetween a first filter port (FP1) and a second filter port (FP2).Sub-filter 2 820-2 is connected between FP1 and a third filter port(FP3). Sub-filter 3 820-3 is connected between FP1 and a fourth filterport (FP4). The array 810 of sub-filters is terminated at both ends byXBARs XL and XH as previously described. FP1 is the common or input portof the multiplexer and FP2, FP3, and FP4 are branch or output ports ofthe multiplexer. A multiplexer may have more than three branch ports. Amultiplexer with two branch ports is commonly referred to as a“diplexer” and a multiplexer with three branch ports may be referred toas a “triplexer”.

FIG. 9 is a graph 900 of the performance of an example of the functionsof an embodiment of the triplexer filter 800 of FIG. 8 . In thisexample, XL, XH, and the three sub-filters are the same as thecorresponding elements of the matrix filter 300 of FIG. 3A. In FIG. 9 ,the solid line under 910 is a plot of S21, the FP1 to FP2 transferfunction, as a function of frequency. The dashed line under 920 is aplot of S31, the FP1 to FP3 transfer function, as a function offrequency. The dotted line under 930 is a plot of S41, the FP1 to FP4transfer function, as a function of frequency. Since the exemplaryfilter is symmetrical, the solid line under 910, the dashed line under920, and the dotted line under 930 are also plots of S12, S13 and S14,respectively.

FP1 may be considered the common port of the matrix filter. FP2 may beconsidered the “low band” port, FP3 may be considered the “middle band”port and FP4 may be considered the “high band” port. When the matrixfilter is used in a frequency division duplex (FDD) radio, one of FP2,FP3 and FP4 may be the receive port and another of FP2, FP3 and FP4 maybe the transmit port depending on the frequencies allocated forreception and transmission. In other cases, in a FDD radio, two of FP2,FP3 and FP4 may be the receive port and the other of FP2, FP3 and FP4may be the transmit port; or vice versa.

In additional multiplexer configurations that are variants of filter800, any one or more of sub-filter 1 820-1, sub-filter 2 820-2, andsub-filter 3 820-3 may be connected in parallel between FP1 and FP2, FP3and/or FP4. In this case, a graph of the performance of an example ofthe matrix filter diplexer has the corresponding ones of the solid,dashed and dotted lines 410, 420 and/or 430 as a plot of S21, S31 and/orS41, as a function of frequency.

The multiplexer filter 800 and two variants may be switched matrixfilters because any one or more of the ports FP2, FP3 and FP4 may beselected or switched to as an output for the filter. For example, thesub-filters connections between input and output ports can be switchedin and out to provide numerous passbands for input and output RFcommunication signals. In one example, a switched XBAR matrix filterhaving 3 sub-filters for LTE bands 3, 1, and 7 provides a multi-passbandreconfigurable filter that is configurable for all 7 possible states:only 1, only 3, only 7, 1+3, 1+7, 3+7, and 1+3+7. This filter has lowloss due to its matrix architecture, such as due to the location of theswitches and due to the filter not needing inductors. This filter alsohas output impedance matched to LNA, so that there is no externalimpedance matching required.

For example, FIG. 10A is a schematic diagram of a reconfigurableswitched matrix filter 1000 using XBARs. The reconfigurable switchedmatrix filter 1000 includes an array 1010 of n sub-filter/switchcircuits 1020-1, 1020-2, 1020-n connected in parallel between a firstfilter port (FP1) and a second filter port (FP2), where n is an integergreater than one. In a subsequent example, n =3. In other cases, n canbe greater than 3 as necessary to provide the desired bandwidth for thereconfigurable matrix filter 1000. Each sub-filter/switch circuitfunctions as a noncontiguous bandpass filter that can be selectivelyenabled (i.e. connected between FP1 and FP2) or disabled (i.e. notconnected between FP1 and FP2). The array 1010 of sub-filter/switchcircuits is terminated at both ends by XBARs XL and XH as previouslydescribed.

The sub-filter/switch circuits 1020-1, 1020-2, 1020-n have noncontiguouspassbands such that the bandwidth of the matrix filter 1000, when allsub-filter/switch modules are enabled, is not equal to the sum of thebandwidths of the constituent sub-filters, but instead has threeseparate and independent passbands separated by stop bands that existwhere the input-output transfer function of the matrix filter 300 isless than −20 dB. One or more of the sub-filter/switch circuits can bedisabled to tailor the matrix filter bandwidth or to insert notches orstop bands within the overall passband, such as to provide the desirednoncontiguous passbands for the matrix filter. The filter 1000 and/orsub-filters may be RF filters that pass frequency bands defined by the5G NR standard.

FIG. 10B is a schematic diagram of a sub-filter/switch circuit 1050suitable for sub-filter/switch circuits 1020-1, 1020-2, and 1020-n inFIG. 10A. The sub-filter/switch circuit 1050 includes three acousticresonators X1, X2, X3 in series between a first sub-filter port (SP1)and a second sub-filter port (SP2), and coupling capacitors C1, C2connected from the junctions between adjacent acoustic resonators toground. The inclusion of three acoustic resonators in thesub-filter/switch circuit 1050 is exemplary, and a sub-filter/switchcircuit may have more than three acoustic resonators. When asub-filter/switch circuit includes more than three acoustic resonators,the number of coupling capacitors will be one less than the number ofacoustic resonators. The acoustic resonators X1, X2, X3 are preferablybut not necessarily XBARs.

The sub-filter/switch circuit 1050 includes a switch SW1 in parallelwith the first shunt capacitor C1 and a switch SW2 in parallel with thelast shunt capacitor C2. When the switches SW1 and SW2 are open, thesub-filter/switch circuit operates as a sub-filter suitable for use inany of the prior examples. In this case, the sub-filter/switch circuitconnection between input and output ports is switched in to provide thepassband of that sub-filter for input and output RF communicationsignals. When the switches SW1 and SW2 are closed, the sub-filter/switchcircuit presents the proper impedance to SP1 and SP2 but has theinput-output transfer function of an open circuit. In this case, thesub-filter/switch circuit connection between input and output ports isswitched out and does not provide the passband of that sub-filter forinput and output RF communication signals.

When a sub-filter/switch circuit includes more than two shuntcapacitors, the switches are in parallel with the two shunt capacitorsimmediately adjacent to the acoustic resonators connected to the twosub-filter ports. In other words, the switches are in parallel with the“first shunt capacitor” and the “last shunt capacitor” that are not inthe middle of the string of resonators, but are just inside of the two“end acoustic resonators” at the ends of the string. In some cases,filter 1000 may be described has having respective output ports SP2 ofall of its sub-filters connected to a common output port FP2. Forexample, the first switch is in parallel with the first capacitor shuntelement that is between an XBAR series element that is immediatelyadjacent to the filter input port and an XBAR series element that isfarther from the input port; and the second switch is in parallelwherein the last capacitor shunt element that is between an XBAR serieselement that is immediately adjacent to the filter output port and anXBAR series element that is farther from the output port.

FIG. 11 is a graph 1100 of the performance 1105 of an example of thereconfigurable switched matrix filter diplexer 1000 of FIG. 10 . In thisexample, XL, XH, and the components within the three sub-filter/switchcircuits are the same as the corresponding elements of the matrix filter300 of FIG. 3A. In FIG. 11 , the solid line under 1110 is a plot of S21,the port 1 to port 2 transfer function, of the filter as a function offrequency when sub-filter/switch circuit 1 is enabled andsub-filter/switch circuit 2 and 3 are disabled. The dashed line under1120 is a plot of S21 as a function of frequency when sub-filter/switchcircuit 2 is enabled and sub-filter/switch circuit 1 and 3 are disabled.The dashed line under 1130 is a plot of S21 as a function of frequencywhen sub-filter/switch circuit 3 is enabled and sub-filter/switchcircuit 1 and 2 are disabled. The sum of the two curves under 1110 and1130, not shown but easily envisioned, is the port 1 to port 2 transferfunction as a function of frequency when sub-filter/switch circuits 1and 3 are enabled and sub-filter/switch circuit 2 is disabled. The sumof the two curves under 1110 and 1120, is the port 1 to port 2 transferfunction as a function of frequency when sub-filter/switch circuits 1and 2 are enabled and sub-filter/switch circuit 3 is disabled. The sumof the two curves under 1110 and 1130, is the port 1 to port 2 transferfunction as a function of frequency when sub-filter/switch circuits 1and 3 are enabled and sub-filter/switch circuit 2 is disabled. The sumof the two curves under 1120 and 1130, is the port 1 to port 2 transferfunction as a function of frequency when sub-filter/switch circuits 2and 3 are enabled and sub-filter/switch circuit 1 is disabled. The sumof the three curves under 1110, 1120 and 1130, is the port 1 to port 2transfer function as a function of frequency when sub-filter/switchcircuits 1, 2 and 3 are enabled. The input-output transfer function ofan open circuit is the port 1 to port 2 transfer function as a functionof frequency when all of the sub-filter/switch circuits 1, 2 and 3 aredisabled. A total of eight different filter configurations are possibleby enabling various combinations of the three sub-filter/switchcircuits.

FIG. 12 is a schematic block diagram of a three-band time divisionduplex (TDD) radio 1200 using a switched matrix triplexer. A TDD radiotransmits and receives in the same frequency channel within a designatedcommunications band. The radio 1200 includes a switched matrix triplexer1210 having a first filter port FP1 configured to connect to an antenna1205 and a second filter port FP2 coupled to a transmit/receive (T/R)switch 1215. The switched matrix bandpass filter 1210 may be, forexample, the switched matrix bandpass filter of FIG. 10A. The T/R switch1215 connects the second port of the matrix bandpass filter 1210 toeither the output of a transmitter 1220 or the input of a receiver 1225.The T/R switch 1215, the transmitter 1220, and the receiver 1225 aresupervised by a processor 1230 performing a media access controlfunction. Specifically, the processor 1230 controls the operation of theT/R switch 1215 and, the switched matrix bandpass filter 1210. When theswitched matrix bandpass filter 1210 is reconfigurable, the processor1230 may control the operation of switches within the bandpass filter.The antenna 1205 may be a part of the radio 1200 or external to theradio 1200.

The radio 1200 is configured for operation in three designatedcommunications bands. The switched matrix bandpass filter 1210 hasinternal switches that allow selection of one of three passbands thatencompasses the designated communications bands and one or more stopbands to block designated frequencies outside of the designatedcommunications bands. Preferably, the switched bandpass filter 1210 haslow loss in its passbands and high rejection in its stop band(s).Further, the switched bandpass filter 1210 must be compatible with TDDoperation, which is to say stable and reliable while passing the RFpower generated by the transmitter 1220. The switched matrix bandpassfilter 1210 may be the switched matrix filter 300 of FIG. 3A or thereconfigurable switched matrix filter 1000 of FIG. 10A implemented usingacoustic resonators which may be XBARs.

The switched matrix bandpass filter 1210 may be a reconfigurable matrixfilter as shown in FIG. 10A. The use of a reconfigurable filter wouldallow the bandwidth of the filter to be set to a single LTE or 5G NRband, allowing the same transmitter and receiver to be used for threeseparate bands. The switches within the sub-filters may be controlled bythe processor 1230.

FIG. 13 is a schematic block diagram of a three-band diversity receiver1300 using a matrix triplexer. A three-band diversity receiver radioreceives in three different frequency ranges corresponding to threecommunications band. The receiver 1300 includes an antenna 1305, amatrix filter triplexer 1310 having a common filter port FP1 configuredto connect to an antenna 1305, a first receiver filter port FP2 coupledto the input of a receiver 1320, a second receiver filter port FP3coupled to the input of a receiver 1325, and a third receive filter portFP4 coupled to the input of a receiver 1330.

The receiver 1300 is configured for operation in the designatedcommunications band. The matrix filter triplexer 1310 includes a receivefilter coupled between each of: FP1 and FP2; FP1 and FP3; and FP1 andF4. The receive filter includes noncontiguous passband receivesub-filters. The matrix filter triplexer 1310 may be implemented usingacoustic resonators which may be XBARs.

The matrix filter diplexer 1310 may be the matrix triplexer 800 of FIG.8 . The FP1, FP2, FP3 and FP4 ports of the matrix filter diplexer 1310may be the FP1, FP2, FP3 and FP4 ports of the matrix multiplexer 800.

In another case, the matrix filter diplexer 1310 may be similar to thereconfigurable switched filter 1000 of FIG. 10A with an equal number ofsub-filters in the transmit and receive filters. The FP1 port of thematrix filter diplexer 1310 may be FP1 of the reconfigurable switchedfilter 1000; and the FP2, FP3 and FP4 ports of the matrix filterdiplexer 1310 may be FP2 of the reconfigurable switched filter 1000.

The acoustic resonator matrix filter topologies herein, such as offilter 300, 600, 800 and/or 1000, may reduce the size of resonators inthe filters, thus: lowering the cost of components for and ofmanufacturing of the filters; provide filter with passbands that arevery insensitive to switch loss; provide filters having achievableimpedance transformation for matching impedance at the input and outputof the filter; and provide filters that are matched to the minimum noisefigure of output connected LNAs without any matching inductor. Thesetopologies allow switching in and out of multiple passbands for inputand output RF communication signals without requiring inductors, such asbetween the coupling capacitors and ground, In one example, an XBARmatrix filter having 3 sub-filters for LTE bands 3, 1, and 7 provides amulti-passband reconfigurable filter that is configurable for all 7possible states: only 1, only 3, only 7, 1+3, 1+7, 3+7, and 1+3+7. Thisfilter has low loss due to its matrix architecture, such as due to thelocation of the switches and due to the filter not needing inductors.This filter also has output impedance matched to LNA, so that there isno external impedance matching required.

Closing Comments

Throughout this description, the embodiments and examples shown shouldbe considered as exemplars, rather than limitations on the apparatus andprocedures disclosed or claimed. Although many of the examples presentedherein involve specific combinations of method acts or system elements,it should be understood that those acts and those elements may becombined in other ways to accomplish the same objectives. With regard toflowcharts, additional and fewer steps may be taken, and the steps asshown may be combined or further refined to achieve the methodsdescribed herein. Acts, elements and features discussed only inconnection with one embodiment are not intended to be excluded from asimilar role in other embodiments.

As used herein, “plurality” means two or more. As used herein, a “set”of items may include one or more of such items. As used herein, whetherin the written description or the claims, the terms “comprising”,“including”, “carrying”, “having”, “containing”, “involving”, and thelike are to be understood to be open-ended, i.e., to mean including butnot limited to. Only the transitional phrases “consisting of” and“consisting essentially of”, respectively, are closed or semi-closedtransitional phrases with respect to claims. Use of ordinal terms suchas “first”, “second”, “third”, etc., in the claims to modify a claimelement does not by itself connote any priority, precedence, or order ofone claim element over another or the temporal order in which acts of amethod are performed, but are used merely as labels to distinguish oneclaim element having a certain name from another element having a samename (but for use of the ordinal term) to distinguish the claimelements. As used herein, “and/or” means that the listed items arealternatives, but the alternatives also include any combination of thelisted items.

It is claimed:
 1. A matrix filter, comprising: a filter input port; andtwo or more sub-filters connected between the filter input port andrespective filter output ports, each sub-filter comprising ntransversely-excited film bulk acoustic resonator (XBAR) series elementsand at least one capacitor shunt elements, where n, the order of thesub-filter, is an integer greater than 2, wherein each sub-filterfurther comprises at least one switch in parallel with the at least onecapacitor shunt elements.
 2. The filter of claim 1, wherein the two ormore sub-filters have noncontiguous passbands; and wherein each of thenoncontiguous passbands is the passband of only one sub-filter.
 3. Thefilter of claim 2, wherein the two or more sub-filters have contiguouspassbands.
 4. The filter of claim 1, wherein only one of the two or moresub-filters is selected to be connected between the filter input portand respective filter output ports; and wherein no single sub-filter'sinput-output transfer function crosses another sub-filter's input-outputtransfer function at a frequency where both filters' transfer functionsare above −20 dB.
 5. The filter of claim 1, wherein each of the two ormore sub-filters have noncontiguous passbands separated by a stop bandthat exists where the input-output transfer function of the matrixfilter is less than −20 dB; and wherein sub-filters connections betweenthe filter input and the respective filter output ports can be switchedto select one or more of the noncontiguous passbands.
 6. The filter ofclaim 1, wherein the at least one capacitor shunt element is between oneof a) an XBAR series element that is immediately adjacent to the filterinput port and an XBAR series element that is farther from the filterinput port; or b) an XBAR series element that is immediately adjacent toa respective filter output port an XBAR series element that is fartherfrom the respective filter output.
 7. The filter of claim 6, wherein theXBAR series elements include a first end XBAR connected to a firstsub-filter port, a second end XBAR connected to a second sub-filterport, and one or more middle XBARs connected between the first andsecond end acoustic resonator.
 8. The filter of claim 1, wherein eachrespective filter output port is connected to a common output port. 9.The filter of claim 1, wherein each of the XBAR series elements isconnected in series between a first sub-filter port and a secondsub-filter port; each of the at least one shunt capacitors is connectedbetween ground and a node between a respective pair of XBAR serieselements; and each of the at least one switches is connected betweenground and the node between the respective pair of XBAR series elements.10. A filter, comprising: a first filter port and a second filter port;n sub-filters, where n is an integer greater than one, each of the nsub-filters having a first sub-filter port connected to the first filterport and a second sub-filter port connected to the second filter port;wherein each sub-filter comprises at least three transversely-excitedfilm bulk acoustic resonator (XBAR) series elements and at least onecapacitor shunt elements; wherein each of the n sub-filters furthercomprise at least one switch in parallel with the at least one capacitorshunt element.
 11. The filter of claim 10, wherein the n sub-filtershave noncontiguous passbands; and wherein each of the noncontiguouspassbands is the passband of only one sub-filter.
 12. The filter ofclaim 10, wherein each of the n sub-filters has a noncontiguous passbandseparated from the passband of all of the other n sub-filters by a stopband that exists where the input-output transfer function of the matrixfilter is less than −20 dB.
 13. The filter of claim 10, wherein only oneof the n sub-filters is selected to be connected between the firstfilter port and the second filter port; and wherein no singlesub-filter's input-output transfer function crosses another sub-filter'sinput-output transfer function at a frequency where both filters'transfer functions are above −20 dB.
 14. The filter of claim 10, whereinthe passband of the filter is selected to be equal to only one of thenoncontiguous passbands of the n sub-filters.
 15. The filter of claim10, wherein each of the XBAR series elements is connected in seriesbetween the first sub-filter port and the second sub-filter port; eachof the at least one shunt capacitors is connected between ground and anode between a respective pair of XBAR series elements; and each of theat least one switches is connected between ground and the node betweenthe respective pair of XBAR series elements.
 16. The filter of claim 15,wherein the XBAR series elements include a first end XBAR connected tothe first sub-filter port, a second end XBAR connected to the secondsub-filter port, and one or more middle XBARs connected between thefirst and second end acoustic resonator, and the at least one capacitorshunt element is between one of a) an XBAR series element that isimmediately adjacent to the first sub-filter port and an XBAR serieselement that is farther from the first sub-filter port; or b) an XBARseries element that is immediately adjacent to the second sub-filterport and an XBAR series element that is farther from the secondsub-filter port.
 17. A three-band diversity receiver, comprising: amatrix triplexer coupled between and antenna and three receivers, thetriplexer comprising; a first sub-filter coupled between a first filterport and a second filter port coupled to the first receiver; a secondsub-filter coupled between the first filter port and a third filter portcoupled to the second receiver; a third sub-filter coupled between thefirst filter port and a fourth filter port coupled to the thirdreceiver; wherein each sub-filter comprises at least threetransversely-excited film bulk acoustic resonator (XBAR) series elementsand at least one capacitor shunt element; wherein each sub-filterfurther comprises at least one switch in parallel with the at least onecapacitor shunt element.
 18. The filter of claim 17, wherein the first,second and third sub-filters each have a noncontiguous passbandseparated from the passband of all of the others of the first, secondand third sub-filters by a stop band that exists where the input-outputtransfer function of the matrix filter is less than −20 dB.
 19. Thefilter of claim 17, wherein each of the XBAR series elements isconnected in series between the first sub-filter port and the secondsub-filter port; each of the at least one shunt capacitors is connectedbetween ground and a node between a respective pair of XBAR serieselements; and each of the at least one switches is connected betweenground and the node between the respective pair of XBAR series elements.20. The filter of claim 17, wherein the first, second and thirdsub-filters have contiguous passbands.